In manufacturing processes of a circuit board, it is required to inspect the presence of disconnection and/or short-circuit in conductive patterns formed on a circuit board.
As to a technique for inspecting a conductive pattern, there has been known a contact type inspection technique comprising bringing two pins into contact, respectively, with both ends of a conductive patter, supplying an electrical signal from one of the pins, and receiving the electrical signal by the other pin to inspect the presence of disconnection or the like in the conductive pattern.
The recent progressive densification of conductive patterns causes difficulties in assuring a sufficient space for simultaneously arranging a plurality of pins, respectively, at the ends of adjacent conductive patterns and bringing the pins into contact with the corresponding ends of the conductive patterns. In view of such circumstances, there has been proposed a non-contact type inspection technique allowing electric signals from conductive patterns to be received in a non-contact manner without using any pin (see Japanese Patent Laid-Open Publication No. Hei 9-264919).
As is shown in FIG. 8, this non-contact type inspection technique comprises bringing a pin into contact with one of the ends of a specific conductive pattern or circuit wiring to be inspected (hereinafter referred to as “target conductive pattern” or “target circuit wiring”), placing a sensor conductor at the other end of the target conductive pattern in non-contact manner, supplying an inspection signal from the pin, and detecting potential variation in conductive pattern using the sensor conductor to inspect the presence of disconnection or the like in the target conductive pattern. More specifically, as shown in FIG. 9 representing an equivalent circuit thereof, disconnection and/or short-circuit in the conductive pattern opposed to the sensor conductor are detected based on the magnitude of an amplified current obtained by amplifying a current generated on the sensor conductor using an amplifier circuit.
In the above conventional non-contact inspection technique, an electromagnetic wave from a conductive pattern has been received by an electrode having a size covering over a plurality of pattern lines on a typical printed circuit board. Thus, it has been impossible to inspect a circuit pattern in the level of 50 μm with a high degree of resolution, and to detect a chipping in a conductive pattern even if it has a relatively large size.